1. Field
Embodiments of the present invention relate to image sensors and, in particular, to correction of defective pixels in image sensors.
2. Discussion of Related Art
A conventional image sensor, which may be fabricated using a complementary metal oxide semiconductor (CMOS) technology or charge coupled device (CCD) technology, includes an array of pixels and associated readout circuitry. A pixel of a typical conventional CMOS image sensor may include a photosensitive element, a micro-lens, one or more light filters, a transfer transistor, a floating diffusion region, reset transistor, source follower, and a row select transistor.
The image sensor generally operates as follows. Light is incident on the micro-lens. The micro-lens focuses the light to the photosensitive element through the light filter. The photosensitive element converts the light into an electrical signal proportional to the intensity of the light detected. The transfer transistor is between the photosensitive element and the floating diffusion region and is used to transfer the electrical signal from the photosensitive element to the floating diffusion region. The electrical signal modulates the source follower. The reset transistor resets the photosensitive element. Keeping in mind that an image sensor array typically includes a large number of pixels, readout circuitry allows signals generated in the photosensitive elements to be processed into a usable image.
Conventional image sensors suffer from some limitations, however. One of the significant factors affecting the performance and yield of color image sensor devices is defective pixels, which may be caused by processing defects, for example. Defective pixels are those pixels in image sensors that fail to sense light correctly. A pixel may produce an electrical signal whose intensity is higher or lower than its neighboring pixels when exposed to a similar light source.